Polychromatic Light Out-coupling Apparatus, Near-eye Displays Comprising the Same, and Method of Out-coupling Polychromatic Light

ABSTRACT

The present invention provides an apparatus including a first out-coupling diffractive optical element and a second out-coupling diffractive optical element. Each of the first and second out-coupling diffractive optical elements includes a first region having a first repeated diffraction spacing, d1, and a second region adjacent to the first region having a second repeated diffraction spacing, d2, different from the first spacing, d1. The first region of the first out-coupling diffractive optical element is superposed on and aligned with the second region of the second out-coupling diffractive optical element. The second region of the first out-coupling diffractive optical element is superposed on and aligned with the first region of the second out-coupling diffractive optical element.

TECHNOLOGICAL FIELD

Embodiments of the present invention relate to a polychromatic lightout-coupling apparatus, near-eye displays comprising the same, and amethod of out-coupling polychromatic light. In particular, they relateto monocular and binocular near-eye displays comprising such apolychromatic light out-coupling apparatus providing a wide field ofview, and to a method of using the same to view a pattern ofpolychromatic light, such as a colour image or a colour video imagesequence.

BACKGROUND

FIGS. 1A and 1B schematically show light 5 entering from the left into adiffractive optical element 10 comprising a diffractive layer 11 havinga repeated diffraction spacing, d. The light 5 is transmitted throughthe interior of the diffractive optical element 10 by total internalreflection and is diffracted by the diffractive layer 11. Whendiffracted, some of the light 5 is out-coupled from the diffractiveoptical element 10, as represented by arrows 15. The angles θ_(n) of theout-coupled light for each diffracted order n are determined by thewavelength λ of the light source and the repeated diffraction spacing dof the diffractive layer 11 according to the well-known equation:

d(sin θ_(n)+sin θ_(i))=nλ  [Eqn. 1]

where θ_(i) is the angle of incident light, n is an integer, θ_(n) isthe angle of the diffracted light and λ is the wavelength of the light.As shown in FIG. 1A, incoming light 5 entering the diffractive opticalelement 10 at smaller angles generally travels a lesser distance by eachtotal internal reflection before being out-coupled by diffraction, sothat the out-coupled light 15 is mostly concentrated near to where thelight has entered the diffractive optical element 10, fading out rapidlyfrom left to right. On the other hand, as shown in FIG. 1B, incominglight 5 entering the diffractive optical element 10 at larger angles cantravel a greater distance by each total internal reflection before beingout-coupled by diffraction, so that the out-coupled light 15 is mostlyconcentrated far from where the light has entered the diffractiveoptical element 10. Similar considerations would apply in a left-rightmirror image if the incoming light 5 were instead to enter thediffractive optical element 10 from the right in FIGS. 1A and 1B, ratherthan from the left.

FIG. 1C schematically shows a pair of such out-coupling diffractiveoptical elements 10L, 10R, each of which comprises a respectivediffractive layer 11L, 11R. The out-coupling diffractive opticalelements 10L, 10R are arranged in optical communication with anin-coupling diffractive optical element 30 comprising a similardiffractive layer 31 to that of the out-coupling diffractive opticalelements 10L, 10R and having the same repeated diffraction spacing d.The in-coupling diffractive optical element 30 receives incoming light5, which is diffracted by diffractive layer 31 and transmitted by totalinternal reflection to the out-coupling diffractive optical elements10L, 10R.

FIG. 1C also schematically shows eyeballs 81, 82 of a viewer gazing atthe out-coupling diffractive optical elements 10L, 10R. As may beunderstood from FIG. 1A, for a viewer looking to the right, as shown inFIG. 1C, the out-coupled light 15 will therefore have lowered brightnessin the region A, whereas light in the region B will fall outside thegaze of the viewer and be wasted. On the other hand, as may also beunderstood from FIG. 1B, for a viewer looking to the left, theout-coupled light 15 will similarly have lowered brightness in theregion B and will fall outside the gaze of the viewer in region A and bewasted.

FIG. 2A schematically shows a pair of components 1, 2 of an apparatusfor out-coupling polychromatic light, for use, for example, in abinocular near-eye display. By polychromatic light is meant light of atleast two different wavelengths. The components 1, 2 each have left andright halves which are mirror images of each other, configured toout-couple light to a pair of eyes. Component 1 therefore comprises apair of out-coupling diffractive optical elements 10L, 10R, a pair ofcorresponding in-coupling diffractive optical elements 30L, 30R, and apair of intermediate optical elements 51, 52, which respectively directlight from the in-coupling diffractive optical element 30L to theout-coupling diffractive optical element 10L and from the in-couplingdiffractive optical element 30R to the out-coupling diffractive opticalelement 10R. Component 2 similarly comprises a pair of out-couplingdiffractive optical elements 20L, 20R, a pair of correspondingin-coupling diffractive optical elements 40L, 40R, and a pair ofintermediate optical elements 53, 54, which respectively direct lightfrom the in-coupling diffractive optical element 40L to the out-couplingdiffractive optical element 20L and from the in-coupling diffractiveoptical element 40R to the out-coupling diffractive optical element 20R.

Components 1 and 2 differ from each other in that the in- andout-coupling diffractive optical elements 30L, 30R, 10L, 10R ofcomponent 1 have a first repeated diffraction spacing, d₁, whereas thein- and out-coupling diffractive optical elements 40L, 40R, 20L, 20R ofcomponent 2 have a second repeated diffraction spacing, d₂, which isdifferent from the first spacing, d₁. Components 1 and 2 can thereforeprovide respective channels of optimized efficiency for diffractinglight in two different wavelength bands. For example, component 1 mayprovide a channel for red light and component 2 may provide a channelfor green-blue light. Thus if components 1 and 2 are superposed one ontop of the other, as is schematically represented in FIG. 2B, and if theoptical elements of each component are carefully aligned, polychromaticlight from a single display can be projected into the in-couplingdiffractive optical elements 30L, 30R, 40L, 40R. Light in two differentwavelength bands will then be out-coupled from elements 10L and 20L andwill re-combine to provide polychromatic light to a viewer's left eye,whilst light in two different wavelength bands will also be out-coupledfrom elements 10R and 20R and re-combine to provide polychromatic lightto the viewer's right eye. A similar arrangement can be used in amonocular near-eye display to out-couple polychromatic light to a singleeye by using only a left or right half of each of the components 1 and2.

The components 1, 2 may each be understood as being similar inconstruction and function to the in- and out-coupling diffractiveoptical elements described above in relation to FIG. 1C. Therefore, theysuffer from the same problems as were explained above in relation toFIG. 1C. Typically, for example, if the components 1, 2 are incorporatedinto a binocular near-eye display, they will provide a field of view ofless than about 40 degrees. The “eye box” can be increased by scalingthe size of all of the optical elements, starting with the display, butthis is undesirable, from the point of view not only of cost, but alsoof wearability. On the other hand, a much wider field of view would behighly desirable, considering that the natural field of view of ahealthy human can extend beyond 180 degrees in the horizontal direction.

BRIEF SUMMARY

According to various, but not necessarily all, embodiments of theinvention there is provided an apparatus comprising a first out-couplingdiffractive optical element and a second out-coupling diffractiveoptical element. Each of the first and second out-coupling diffractiveoptical elements comprises a first region having a first repeateddiffraction spacing, d₁, and a second region adjacent to the firstregion having a second repeated diffraction spacing, d₂, different fromthe first spacing, d₁. The first region of the first out-couplingdiffractive optical element is superposed on and aligned with the secondregion of the second out-coupling diffractive optical element. Thesecond region of the first out-coupling diffractive optical element issuperposed on and aligned with the first region of the secondout-coupling diffractive optical element.

With such an apparatus, light of two different wavelengths from twodifferent respective in-coupling diffractive optical elements can bedirected into one and the same out-coupling diffractive optical elementfrom different locations and/or directions for viewing by a single eye.Light of one of the two wavelengths is out-coupled from the first regionof the out-coupling diffractive optical element, whereas light of theother of the two wavelengths is out-coupled from the second region ofthe same out-coupling diffractive optical element. Thus if two suchout-coupling diffractive optical elements are superposed one on top ofthe other, with the first region of the first out-coupling diffractiveoptical element carefully aligned with the second region of the secondout-coupling diffractive optical element, and with the second region ofthe first out-coupling diffractive optical element carefully alignedwith the first region of the second out-coupling diffractive opticalelement, a viewer can see polychromatic light in a field of view whichis much wider than from an arrangement such as shown and described abovein relation to FIGS. 2A and 2B. The resulting technical effect may alsobe understood as allowing polychromatic light to be coupled into the twosuperposed out-coupling diffractive optical elements from two differentlocations and/or directions, for example from opposing directions. Thusregardless of whether the viewer is looking to the left or to the right,they will always be able to view polychromatic light which has nottravelled far through the two out-coupling diffractive optical elementsby total internal reflection from a respective one of the in-couplingdiffractive optical elements before the light is out-coupled bydiffraction from the corresponding region of one of the two out-couplingdiffractive optical elements. The out-coupled light is therefore lesssubject to fade-out or vignetting at viewing angles which are much widerthan conventionally. In principle, all other things being equal, thefield of view could be doubled in comparison to a conventionalarrangement, although the actual field of view can be optimizedaccording to ergonomic requirements and other design considerations.

Preferably, the first and second out-coupling diffractive opticalelements are both substantially rectangular and have a pair of longedges and a pair of short edges, and a division between the first regionand the second region of the first and second out-coupling diffractiveoptical elements is located substantially equidistant between the pairof short edges. Thus, according to such an embodiment, the eye of aviewer of the first and second out-coupling diffractive optical elementsmay be positioned substantially perpendicular to the division, for equalviewing of the first and second regions.

The length of the long edges of the first and second out-couplingdiffractive optical elements may be different between differentembodiments, but the division between the first region and the secondregion should nonetheless be maintained substantially equidistant fromeach of the pair of short edges between the different embodiments.

Any of the diffractive optical elements may, for example, be a hologram,such as a volume hologram, or a diffraction grating, such as a surfacerelief diffraction grating. By “repeated diffraction spacing” is meantthe separation between repeated diffractive features of a diffractiveoptical element. The repeated diffractive features may be orientedparallel to each other in any preferred direction. For example, if thediffractive optical elements are to be incorporated into a near-eyedisplay, the repeated diffractive features may preferably be orientedsuch that in use of the near-eye display, they will be substantiallyparallel to either a vertical or a horizontal axis of the display.

If the first and second out-coupling diffractive optical elements areboth diffraction gratings, the first region of each grating may compriserulings of the first spacing, d₁, and the second region of each gratingmay comprise rulings of the second spacing, d₂. Preferably, the rulingsof the first region of each grating are substantially parallel to therulings of the second region of the same grating. This has the advantageof allowing for easy manufacture of each of the first and secondout-coupling diffractive optical elements by ruling them in a singlemanufacturing operation. In an alternative preferred embodiment, therulings of the first region of each grating may instead be substantiallyperpendicular to the rulings of the second region of the same grating.This has the advantage of allowing light to be directed into eachgrating region from directions which are perpendicular to each other,giving greater design freedom to adapt to ergonomic requirements.

Preferably, the apparatus further comprises a first pair of in-couplingdiffractive optical elements having the first repeated diffractionspacing, d1, which are configured to direct light to the first region ofrespective ones of the first and second out-coupling diffractive opticalelements, and a second pair of in-coupling diffractive optical elementshaving the second repeated diffraction spacing, d2, which are configuredto direct light to the second region of respective ones of the first andsecond out-coupling diffractive optical elements.

If so, the apparatus preferably also comprises at least one intermediateoptical element configured to transmit light from a respective one ofthe in-coupling diffractive optical elements to a region of a respectiveone of the out-coupling diffractive optical elements having the samespacing as the respective one of the in-coupling diffractive opticalelements. Such an intermediate optical element may be positioned alongone of the long edges or along one of the short edges of the respectiveone of the out-coupling diffractive optical elements, according to theorientation, relative to the short or long edge, of the repeateddiffractive features of said region having the same spacing as therespective one of the in-coupling diffractive optical elements. Forexample, if the repeated diffractive features of the region are parallelto the long edge of the out-coupling diffractive optical element, thenthe intermediate optical element may be positioned along the long edgeas well. On the other hand, if the repeated diffractive features of theregion are parallel to the short edge of the out-coupling diffractiveoptical element, then the intermediate optical element may be positionedalong the short edge instead. There may be other configurations,depending on the desired form factor of the device to be manufactured.

The at least one intermediate optical element may comprise at least oneof a diffractive optical element, such as a hologram or diffractiongrating, and a reflective optical element, such as a mirror or prism.The at least one intermediate optical element may be configured as awaveguide for light from a respective one of the in-coupling diffractiveoptical elements to a region of a respective one of the out-couplingdiffractive optical elements having the same spacing as the respectiveone of the in-coupling diffractive optical elements. Alternatively oradditionally, the at least one intermediate optical element may beconfigured as a beam expander to expand light from a respective one ofthe in-coupling diffractive optical elements to a region of a respectiveone of the out-coupling diffractive optical elements having the samespacing as the respective one of the in-coupling diffractive opticalelements.

According to various, but not necessarily all, embodiments of theinvention there is also provided a monocular near-eye display comprisingan apparatus as described above, a first optical projection engine and asecond optical projection engine. The first optical projection engine isconfigured to project polychromatic light into the first and secondin-coupling diffractive optical elements which are respectivelyconfigured to direct light to the first region of the first out-couplingdiffractive optical element and to the second region of the secondout-coupling diffractive optical element. The second optical projectionengine is configured to project polychromatic light into the first andsecond in-coupling diffractive optical elements which are respectivelyconfigured to direct light to the first region of the secondout-coupling diffractive optical element and to the second region of thefirst out-coupling diffractive optical element.

Any of the optical projection engines may typically comprise, forexample, a display, such as a microdisplay, and a collimator.

According to various, but not necessarily all, embodiments of theinvention there is also provided a binocular near-eye display comprisingtwo apparatuses as described above, a first optical projection engine, asecond optical projection engine and at least one additional opticalprojection engine. The first optical projection engine is configured toproject polychromatic light into the first and second in-couplingdiffractive optical elements which are respectively configured to directlight to the first region of the first out-coupling diffractive opticalelement and to the second region of the second out-coupling diffractiveoptical element of a first one of the two apparatuses. The secondoptical projection engine is configured to project polychromatic lightinto the first and second in-coupling diffractive optical elements whichare respectively configured to direct light to the first region of thefirst out-coupling diffractive optical element and to the second regionof the second out-coupling diffractive optical element of a second oneof the two apparatuses. The at least one additional optical projectionengine is configured to project polychromatic light into the first andsecond in-coupling diffractive optical elements which are respectivelyconfigured to direct light to the first region of the secondout-coupling diffractive optical element and to the second region of thefirst out-coupling diffractive optical element of at least one of thetwo apparatuses.

Any of the optical projection engines may typically comprise, forexample, a display, such as a microdisplay, and a collimator.

Preferably, each of the two apparatuses of the binocular near-eyedisplay has a respective midpoint, and a separation between themidpoints of the two apparatuses is adjustable, to accommodate differentinterpupillary distances of different users.

Preferably, the at least one additional optical projection enginecomprises a third optical projection engine and a fourth opticalprojection engine. The third optical projection engine is configured toproject polychromatic light into the first and second in-couplingdiffractive optical elements which are respectively configured to directlight to the first region of the second out-coupling diffractive opticalelement and to the second region of the first out-coupling diffractiveoptical element of the first one of the two apparatuses. The fourthoptical projection engine is configured to project polychromatic lightinto the first and second in-coupling diffractive optical elements whichare respectively configured to direct light to the first region of thesecond out-coupling diffractive optical element and to the second regionof the first out-coupling diffractive optical element of the second oneof the two apparatuses.

In an alternative possible preferred embodiment, the at least oneadditional optical projection engine is instead configured to projectpolychromatic light by temporal or spatial interlacing into the firstand second in-coupling diffractive optical elements which arerespectively configured to direct light to the first region of thesecond out-coupling diffractive optical element and to the second regionof the first out-coupling diffractive optical element of both of the twoapparatuses. Thus, for example, the at least one additional opticalprojection engine may project alternate frames of a video image sequenceinto said first and second in-coupling diffractive optical elements bytemporal interlacing, or the at least one additional optical projectionengine may project alternate lines of each frame of a video imagesequence into said first and second in-coupling diffractive opticalelements by spatial interlacing.

According to various, but not necessarily all, embodiments of theinvention there is further provided a method comprising: emitting afirst pattern of light of a first wavelength from a first region of afirst out-coupling diffractive optical element and a second pattern oflight of a second wavelength from a second region of the firstout-coupling diffractive optical element adjacent to the first region;emitting light of the first wavelength in the second pattern from afirst region of a second out-coupling diffractive optical element andlight of the second wavelength in the first pattern from a second regionof the second out-coupling diffractive optical element adjacent to thefirst region; superposing and aligning the first patterns of lightemitted from the first region of the first out-coupling diffractiveoptical element and from the second region of the second out-couplingdiffractive optical element; and superposing and aligning the secondpatterns of light emitted from the second region of the firstout-coupling diffractive optical element and from the first region ofthe second out-coupling diffractive optical element.

Preferably, the first and second patterns of light may typically bespatially continuous with each other, so that together they combine toform a single pattern, such as a single still image or a single frame ofa video sequence.

Preferably, the method further comprises projecting polychromatic lightwith the first pattern into one of a first pair of in-couplingdiffractive optical elements with a first repeated diffraction spacingcorresponding to the first wavelength and into one of a second pair ofin-coupling diffractive optical elements with a second repeateddiffraction spacing corresponding to the second wavelength; projectingpolychromatic light with the second pattern into the other of the firstpair of in-coupling diffractive optical elements with the first repeateddiffraction spacing and into the other of the second pair of in-couplingdiffractive optical elements with the second repeated diffractionspacing; transmitting the first pattern of light from said one of thefirst pair of in-coupling diffractive optical elements to the firstregion of the first out-coupling diffractive optical element and fromsaid one of the second pair of in-coupling diffractive optical elementsto the second region of the second out-coupling diffractive opticalelement; and transmitting the second pattern of light from said other ofthe first pair of in-coupling diffractive optical elements to the firstregion of the second out-coupling diffractive optical element and fromsaid other of the second pair of in-coupling diffractive opticalelements to the second region of the first out-coupling diffractiveoptical element.

BRIEF DESCRIPTION

For a better understanding of various examples that are useful forunderstanding the detailed description, reference will now be made byway of example only to the accompanying drawings in which:

FIG. 1A is a first schematic view showing a longitudinal cross-sectionthrough an out-coupling diffractive optical element;

FIG. 1B is a second schematic view showing a longitudinal cross-sectionthrough the out-coupling diffractive optical element of FIG. 1A;

FIG. 1C is a schematic view showing a longitudinal cross-section throughan apparatus comprising an in-coupling diffractive optical element and apair of out-coupling diffractive optical elements as seen by a viewer;

FIG. 2A is a schematic plan view of two components of a first apparatusfor out-coupling polychromatic light;

FIG. 2B is a schematic plan view of the two components of FIG. 2Asuperposed one on top of the other;

FIG. 3A is a schematic plan view of two components of a second apparatusfor out-coupling polychromatic light;

FIG. 3B is a schematic plan view of the two components of FIG. 3Asuperposed one on top of the other;

FIG. 4A is a schematic plan view of two components of each of a thirdand a fourth apparatus for out-coupling polychromatic light;

FIG. 4B is a schematic plan view of the two components of each of thethird and fourth apparatuses of FIG. 4A superposed one on top of theother;

FIG. 5A is a schematic plan view of a first monocular near-eye display;

FIG. 5B is a first schematic view showing a longitudinal cross-sectionthrough the monocular near-eye display of FIG. 5A;

FIG. 5C is a second schematic view showing a longitudinal cross-sectionthrough the monocular near-eye display of FIG. 5A;

FIG. 6A is a schematic plan view of a second monocular near-eye displayin a first configuration;

FIG. 6B is a schematic view showing a longitudinal cross-section throughthe monocular near-eye display of FIG. 6A in the first configuration;

FIG. 7A is a schematic plan view of the second monocular near-eyedisplay of FIGS. 6A and 6B in a second configuration;

FIG. 7B is a schematic view showing a longitudinal cross-section throughthe monocular near-eye display of FIGS. 6A to 7A in the secondconfiguration; and

FIG. 8 is a flow diagram schematically representing a method ofout-coupling polychromatic light.

DETAILED DESCRIPTION

FIG. 3A shows two components 3A, 3B of an apparatus 3 for out-couplingpolychromatic light. The component 3A comprises a first out-couplingdiffractive optical element 10, a first in-coupling diffractive opticalelement 30 a, a second in-coupling diffractive optical element 30 b, andtwo intermediate optical elements 51, 52. The first out-couplingdiffractive optical element 10 comprises a first region 12 a having afirst repeated diffraction spacing, d₁, and a second region 12 badjacent to the first region 12 a and having a second repeateddiffraction spacing, d₂, which is different from the first spacing, d₁.The first in-coupling diffractive optical element 30 a also has thefirst repeated diffraction spacing, d₁, and is configured to directlight to the first region 12 a. The second in-coupling diffractiveoptical element 30 b instead has the second repeated diffractionspacing, d₂, and is configured to direct light to the second region 12b. The two intermediate optical elements 51, 52 are respectivelyconfigured to transmit light from the first in-coupling diffractiveoptical element 30 a to the first region 12 a and from the secondin-coupling diffractive optical element 30 b to the second region 12 b.

The component 3B comprises a second out-coupling diffractive opticalelement 20, another first in-coupling diffractive optical element 40 a,another second in-coupling diffractive optical element 40 b, and twofurther intermediate optical elements 53, 54. The second out-couplingdiffractive optical element 20 comprises a first region 22 a having thefirst repeated diffraction spacing, d₁, and a second region 22 badjacent to the first region 22 a and having the second repeateddiffraction spacing, d₂. The first in-coupling diffractive opticalelement 40 a also has the first repeated diffraction spacing, d₁, and isconfigured to direct light to the first region 22 a. The secondin-coupling diffractive optical element 40 b instead has the secondrepeated diffraction spacing, d₂, and is configured to direct light tothe second region 22 b. The two intermediate optical elements 53, 54 arerespectively configured to transmit light from the first in-couplingdiffractive optical element 40 a to the first region 22 a and from thesecond in-coupling diffractive optical element 40 b to the second region22 b.

The first and second out-coupling diffractive optical elements 10, 20are both substantially rectangular and have respective long edges 14, 24and short edges 16, 26. A division between the first region 12 a, 22 aand the second region 12 b, 22 b of the first and second out-couplingdiffractive optical elements 10, 20 is located substantially equidistantbetween the pair of short edges. In this embodiment, the first andsecond out-coupling diffractive optical elements 10, 20 are bothdiffraction gratings. The first region 12 a, 22 a of each gratingcomprises rulings of the first spacing, d₁, and the second region 12 b,22 b of each grating comprises rulings of the second spacing, d₂. Therulings of the first region of each grating are substantially parallelto the rulings of the second region of the same grating and are alignedsubstantially parallel with the short edges 16, 26 of the out-couplingdiffractive optical elements 10, 20. All of the intermediate opticalelements 51, 52; 53, 54 are positioned along the short edges 16, 26 ofthe respective ones 10, 20 of the out-coupling diffractive opticalelements.

FIG. 3B shows the two components 3A, 3B of FIG. 3A superposed one on topof the other in apparatus 3. The first region 12 a of the firstout-coupling diffractive optical element 10 is carefully aligned withthe second region 22 b of the second out-coupling diffractive opticalelement 20, and the second region 12 b of the first out-couplingdiffractive optical element 10 is carefully aligned with the firstregion 22 a of the second out-coupling diffractive optical element 20.Thus, if a first pattern of polychromatic light is projected into theleft first and second in-coupling diffractive optical elements 30 a, 40b, the first pattern of light of a first wavelength equal to the firstspacing d₁ will be transmitted from the first in-coupling diffractiveoptical element 30 a by the intermediate optical element 51 to the firstregion 12 a of the first out-coupling diffractive optical element 10,and the first pattern of light of a second wavelength equal to thesecond spacing d₂ will be transmitted from the second in-couplingdiffractive optical element 40 b by the intermediate optical element 53to the second region 22 b of the second out-coupling diffractive opticalelement 20. Thereafter, the first pattern of light of the firstwavelength will be emitted from the first region 12 a of the firstout-coupling diffractive optical element 10, and the first pattern oflight of the second wavelength will be emitted from the second region 22b of the second out-coupling diffractive optical element 20. Due to theaforementioned careful alignment of the optical elements, the firstpattern of light of the first wavelength emitted from the first region12 a and the first pattern of light of the second wavelength emittedfrom the second region 22 b will therefore also be superposed andaligned with each other, and will recombine to recreate the firstpattern of polychromatic light on a left-hand side of a combined fieldof view of the out-coupling diffractive optical elements 10, 20.

Meanwhile, if a second pattern of polychromatic light is projected intothe right first and second in-coupling diffractive optical elements 40a, 30 b, the second pattern of light of the first wavelength will betransmitted from the first in-coupling diffractive optical element 40 aby the intermediate optical element 54 to the first region 22 a of thesecond out-coupling diffractive optical element 20, and the secondpattern of light of the second wavelength will be transmitted from thesecond in-coupling diffractive optical element 30 b by the intermediateoptical element 52 to the second region 12 b of the first out-couplingdiffractive optical element 10. Thereafter, the second pattern of lightof the first wavelength will be emitted from the first region 22 a ofthe second out-coupling diffractive optical element 20, and the secondpattern of light of the second wavelength will be emitted from thesecond region 12 b of the first out-coupling diffractive optical element10. Once again, due to the aforementioned careful alignment of theoptical elements, the second pattern of light of the first wavelengthemitted from the first region 22 a and the second pattern of light ofthe second wavelength emitted from the second region 12 b will also besuperposed and aligned with each other, and will recombine to recreatethe second pattern of polychromatic light on a right-hand side of thecombined field of view of the out-coupling diffractive optical elements10, 20.

If the first pattern of polychromatic light on the left-hand side of thecombined field of view is continuous with the second pattern ofpolychromatic light on the right-hand side of the combined field ofview, the first and second patterns of polychromatic light will combineto create a single pattern of polychromatic light in a field of viewwhich is both wider and brighter than in a conventional arrangement,such as that shown and described above in relation to FIGS. 2A and 2B,for example. In order to achieve this, the first and second patterns ofpolychromatic light do not have to be distinct left and right halves ofone image or sequence of images, with a sharp boundary between the twohalves. Instead, the first and second patterns of polychromatic lightmay just be two copies of the same image or sequence of images. If so,the first pattern will fade out from left to right during its passagethrough the apparatus 3 and the second pattern will fade out from rightto left by a similar amount during its passage through the apparatus 3,so that when the two patterns are recombined as just described, they canform a single pattern of uniform brightness, with little or novignetting.

The apparatus 3 shown in FIG. 3B is suitable for use in a monocularnear-eye display, if combined with a first optical projection engineconfigured to project polychromatic light into the left first and secondin-coupling diffractive optical elements 30 a, 40 b, and with a secondoptical projection engine configured to project polychromatic light intothe right first and second in-coupling diffractive optical elements 40a, 30 b. Two copies of the apparatus 3 shown in FIG. 3B arranged side byside with each other along their short edges would also be suitable foruse in a binocular near-eye display, one for each eye, if combined withat least three optical projection engines, as follows. A first opticalprojection engine configured to project polychromatic light into theleft first and second in-coupling diffractive optical elements 30 a, 40b of a first one of the two apparatuses, a second optical projectionengine configured to project polychromatic light into the right firstand second in-coupling diffractive optical elements 40 a, 30 b of asecond one of the two apparatuses, and at least one additional opticalprojection engine configured to project polychromatic light into theremaining in-coupling diffractive optical elements of the twoapparatuses.

FIG. 4A shows on the left-hand side thereof, two components 4La, 4Lb ofa first apparatus 4L, and on the right-hand side thereof, two components4Ra, 4Rb of a second apparatus 4R, both of which apparatuses are forout-coupling polychromatic light. The two apparatuses 4L, 4R are mirrorimages of each other, so for the sake of concision, only the left-hand,apparatus 4L will be described below, and the structure and function ofthe right-hand apparatus 4R can be readily and clearly understood fromthe same description. The two apparatuses 4L, 4R are suitable for usetogether with each other in a binocular near-eye display, one for eacheye, if combined with suitable optical projection engines, as will bedescribed further below.

The component 4La comprises a first out-coupling diffractive opticalelement 10, a first in-coupling diffractive optical element 30 a, asecond in-coupling diffractive optical element 30 b, and twointermediate optical elements 51, 52. The first out-coupling diffractiveoptical element 10 comprises a first region 12 a having a first repeateddiffraction spacing, d₁, and a second region 12 b adjacent to the firstregion 12 a and having a second repeated diffraction spacing, d₂, whichis different from the first spacing, d₁. The first in-couplingdiffractive optical element 30 a also has the first repeated diffractionspacing, d₁, and is configured to direct light to the first region 12 a.The second in-coupling diffractive optical element 30 b instead has thesecond repeated diffraction spacing, d₂, and is configured to directlight to the second region 12 b. The two intermediate optical elements51, 52 are respectively configured to transmit light from the firstin-coupling diffractive optical element 30 a to the first region 12 aand from the second in-coupling diffractive optical element 30 b to thesecond region 12 b.

The component 4Lb comprises a second out-coupling diffractive opticalelement 20, another first in-coupling diffractive optical element 40 a,another second in-coupling diffractive optical element 40 b, and twofurther intermediate optical elements 53, 54. The second out-couplingdiffractive optical element 20 comprises a first region 22 a having thefirst repeated diffraction spacing, d₁, and a second region 22 badjacent to the first region 22 a and having the second repeateddiffraction spacing, d₂. The first in-coupling diffractive opticalelement 40 a also has the first repeated diffraction spacing, d₁, and isconfigured to direct light to the first region 22 a. The secondin-coupling diffractive optical element 40 b instead has the secondrepeated diffraction spacing, d₂, and is configured to direct light tothe second region 22 b. The two intermediate optical elements 53, 54 arerespectively configured to transmit light from the first in-couplingdiffractive optical element 40 a to the first region 22 a and from thesecond in-coupling diffractive optical element 40 b to the second region22 b.

The first and second out-coupling diffractive optical elements 10, 20are both substantially rectangular and have respective long edges 14, 24and short edges 16, 26. A division between the first region 12 a, 22 aand the second region 12 b, 22 b of the first and second out-couplingdiffractive optical elements 10, 20 is located substantially equidistantbetween the pair of short edges. In this embodiment, the first andsecond out-coupling diffractive optical elements 10, 20 are bothdiffraction gratings. The first region 12 a, 22 a of each gratingcomprises rulings of the first spacing, d₁, and the second region 12 b,22 b of each grating comprises rulings of the second spacing, d₂. Incontrast to the embodiment shown and described above in relation toFIGS. 3A and 3B, the rulings of the first region 12 a, 22 a of eachgrating are substantially perpendicular to the rulings of the secondregion 12 b, 22 b of the same grating. In addition, the rulings of thefirst region 12 a of the first grating 10 and the rulings of the secondregion 22 b of the second grating 20 are aligned substantiallyperpendicular with the short edges 16, 26 of the out-couplingdiffractive optical elements 10, 20. Because of this differentconfiguration of the first region 12 a of the first grating 10 and ofthe second region 22 b of the second grating 20, in contrast to theembodiment shown in FIGS. 3A and 3B, their respective intermediateoptical elements 51, 53 are instead positioned along the long edges 14,24 of the respective ones 10, 20 of the out-coupling diffractive opticalelements. On the other hand, the other intermediate optical elements 52,54 are still positioned along the short edges 16, 26 of the respectiveones 10, 20 of the out-coupling diffractive optical elements, as in theembodiment shown in FIGS. 3A and 3B. This different arrangement of theintermediate optical elements 51, 53 allows light to be directed intoeach grating 10, 20 from directions which are perpendicular to eachother, giving greater design freedom to adapt to ergonomic requirements.

FIG. 4B shows on the left-hand side thereof, the two components 4La, 4Lbof FIG. 4A superposed one on top of the other in apparatus 4L, and onthe right-hand side thereof, the two components 4Ra, 4Rb of FIG. 4Asuperposed one on top of the other in apparatus 4R. As with FIG. 4A,since the two apparatuses 4L, 4R are mirror images of each other, forthe sake of concision, only the left-hand apparatus 4L will be describedbelow, and the structure and function of the right-hand apparatus 4R canbe readily and clearly understood from the same description. In theapparatus 4L, the first region 12 a of the first out-couplingdiffractive optical element 10 is carefully aligned with the secondregion 22 b of the second out-coupling diffractive optical element 20,and the second region 12 b of the first out-coupling diffractive opticalelement 10 is carefully aligned with the first region 22 a of the secondout-coupling diffractive optical element 20. The apparatus 4L istherefore able to function in a similar manner to the apparatus 3described above in relation to FIG. 3B. Thus, if a first pattern ofpolychromatic light is projected into the left first and secondin-coupling diffractive optical elements 30 a, 40 b, and if a secondpattern of polychromatic light is projected into the right first andsecond in-coupling diffractive optical elements 40 a, 30 b, the firstpattern of polychromatic light will be recreated on a left-hand side ofa combined field of view of the out-coupling diffractive opticalelements 10, 20 and the second pattern of polychromatic light will berecreated on a right-hand side of the combined field of view of theout-coupling diffractive optical elements 10, 20. If the first patternof polychromatic light on the left-hand side of the combined field ofview is continuous with the second pattern of polychromatic light on theright-hand side of the combined field of view, the first and secondpatterns of polychromatic light will combine to create a single patternof light in a field of view which is both wider and brighter than in aconventional arrangement, in a similar manner to that described above inrelation to FIG. 3B, with the same technical results and advantages asalready described above.

As mentioned above, the two apparatuses 4L, 4R are suitable for usetogether with each other in a binocular near-eye display, one for eacheye, if combined with suitable optical projection engines. If so, theseoptical projection engines should include a first optical projectionengine configured to project polychromatic light into the left first andsecond in-coupling diffractive optical elements 30 a, 40 b of theleft-hand one 4L of the two apparatuses, a second optical projectionengine configured to project polychromatic light into the right firstand second in-coupling diffractive optical elements 30 a, 40 b of theright-hand one 4R of the two apparatuses, and at least one additionaloptical projection engine configured to project polychromatic light intothe other in-coupling diffractive optical elements 40 a, 30 b of bothapparatuses 4L, 4R.

Each of the two apparatuses 4L, 4R has a respective midpoint ML, MR, ashown in FIG. 4B. If the two apparatuses 4L, 4R are combined withoptical projection engines in a binocular near-eye display as justdescribed, a separation between these two midpoints ML, MR may also bemade adjustable, in order to accommodate different interpupillarydistances 83 (see. FIG. 7B) of different users.

In a first possible alternative embodiment, the at least one additionaloptical projection engine may comprise a third optical projection engineconfigured to project polychromatic light into the first and secondin-coupling diffractive optical elements 40 a, 30 b of the left-handapparatus 4L, and a fourth optical projection engine configured toproject polychromatic light into the first and second in-couplingdiffractive optical elements 40 a, 30 b of the right-hand apparatus 4R.However, in a second possible alternative embodiment, the at least oneadditional optical projection engine may instead be configured toproject polychromatic light by temporal or spatial interlacing into thefirst and second in-coupling diffractive optical elements 40 a, 30 b ofboth of the two apparatuses 4L, 4R. For example, the at least oneadditional optical projection engine may project alternate frames of avideo image sequence into the first and second in-coupling diffractiveoptical elements 40 a, 30 b of both of the two apparatuses 4L, 4R bytemporal interlacing, or the at least one additional optical projectionengine may project alternate lines of each frame of a video imagesequence into the first and second in-coupling diffractive opticalelements 40 a, 30 b of both of the two apparatuses 4L, 4R by spatialinterlacing.

FIGS. 5A and 5B respectively schematically show plan and cross-sectionalviews of a first monocular near-eye display 7 in relation to a viewer 8having eyeballs 81, 82. The monocular near-eye display 7 comprises anoptical projection engine 60, an in-coupling diffractive optical element30, an intermediate optical element 50, and an out-coupling diffractiveoptical element 10. The optical projection engine 60 comprises amicrodisplay 601 and a collimator 602. The out-coupling diffractiveoptical element 10 comprises a diffractive layer having a repeateddiffraction spacing, d. Light 5 from the microdisplay 601 is projectedby the collimator 602 into the in-coupling diffractive optical element30 and is transmitted from there by the intermediate optical element 50to the out-coupling diffractive optical element 10. The light 5 istransmitted through the interior of the diffractive optical element 10by total internal reflection and is diffracted by the diffractive layerthereof. When diffracted, the light 5 is out-coupled from thediffractive optical element 10, as represented by arrows 15. Since theout-coupling diffractive optical element 10 is of a conventional design,similar to that shown and described above in relation to FIGS. 2A and2B, some of the out-coupled light 15 is wasted by falling in regionsindicated in FIG. 5C by the letter C, outside the entrance pupil of eye82.

In contrast, FIGS. 6A and 6B respectively schematically show plan andcross-sectional views of a second monocular near-eye display 9A inrelation to a viewer 8 having eyeballs 81, 82.

The monocular near-eye display 9A comprises two optical projectionengines 61, 62, each of which respectively comprises a microdisplay 611,621 and a collimator 612, 622. The monocular near-eye display 9A furthercomprises an apparatus 3, as described above in relation to FIG. 3B. Theapparatus 3 therefore comprises two pairs of superposed and alignedin-coupling diffractive optical elements 30 a, 40 b and 30 b, 40 a, fourintermediate optical elements 51, 52, 53, 54, and two superposed andaligned out-coupling diffractive optical elements 10, 20. Theout-coupling diffractive optical elements 10, 20 each respectivelycomprise a first region 12 a, 22 a and a second region 12 b, 22 b, withproperties as already described above in relation to FIG. 3B. Thus afirst pattern of polychromatic light 5 a projected by a first one 61 ofthe two optical projection engines into the in-coupling diffractiveoptical elements 30 a, 40 b and a second pattern of polychromatic light5 b projected by a second one 62 of the two optical projection enginesinto the in-coupling diffractive optical elements 30 b, 40 a arecombined with each other by the two superposed and aligned out-couplingdiffractive optical elements 10, 20 to create a single pattern ofpolychromatic light 15 in a field of view which is both wider andbrighter than in a conventional arrangement, such as that shown anddescribed above in relation to FIGS. 5A to 5C. When the two patterns 5a, 5 b are thus recombined, they can therefore form a single pattern ofuniform brightness, with little or no vignetting.

FIGS. 7A and 7B respectively schematically show plan and cross-sectionalviews of a third monocular near-eye display 9B, wherein the length ofthe long edges of the first and second out-coupling diffractive opticalelements 10, 20 is less than that of the long edges of the first andsecond out-coupling diffractive optical elements 10, 20 in the secondmonocular near-eye display 9A, whereas a length of the short edges ofthe first and second out-coupling diffractive optical elements 10, 20remains the same. In other words, an aspect ratio of the first andsecond out-coupling diffractive optical elements 10, 20 in the thirdmonocular near-eye display 9B is less than that of the first and secondout-coupling diffractive optical elements 10, 20 in the second monocularnear-eye display 9A. A separation, s, of the two optical projectionengines 61, 62 has also been correspondingly reduced, in comparison totheir respective dispositions as shown in FIGS. 6A and 6B. On the otherhand, the division between the first and second regions of the first andsecond out-coupling diffractive optical elements 10, 20 has beenmaintained substantially equidistant between the short edges of elements10, 20. Thus, as may be seen in FIG. 7B, the eye of a viewer 8′ of thefirst and second out-coupling diffractive optical elements 10, 20remains positioned substantially perpendicular to this division, forequal viewing of the first and second regions. On the other hand, as maybe seen by comparing the spread of the arrows 15 representingout-coupled light in FIG. 7B with that of the arrows 15 in FIG. 6B, moreof the out-coupled light enters the eye 82 of the viewer 8′ in FIG. 7Bthan enters the eye of the viewer 8 in FIG. 6B, and less of theout-coupled light is wasted. The viewer 8′ therefore experiences animage of improved brightness.

In all of the accompanying drawings, including FIGS. 5A, 6A and 7A, itshould be noted that the orientation of the hatching on the intermediateoptical elements 50, 51, 52, 53, 54 does not necessarily represent theorientation of any repeated diffractive features of the intermediateoptical elements 50, 51, 52, 53, 54.

Finally, FIG. 8 schematically represents a method of out-couplingpolychromatic light. In box 101, polychromatic light with a firstpattern 5 a is projected into one 30 a of a first pair of in-couplingdiffractive optical elements with a first repeated diffraction spacingcorresponding to a first wavelength and into one 40 b of a second pairof in-coupling diffractive optical elements with a second repeateddiffraction spacing corresponding to a second wavelength. Meanwhile, inbox 102, polychromatic light with a second pattern 5 b is projected intothe other 40 a of the first pair of in-coupling diffractive opticalelements with the first repeated diffraction spacing and into the other30 b of the second pair of in-coupling diffractive optical elements withthe second repeated diffraction spacing.

In box 201, the first pattern of light 5 a is transmitted from said one30 a of the first pair of in-coupling diffractive optical elements tothe first region 12 a of the first out-coupling diffractive opticalelement 10 and from said one 40 b of the second pair of in-couplingdiffractive optical elements to the second region 22 b of the secondout-coupling diffractive optical element 20. Meanwhile, in box 202, thesecond pattern of light is transmitted from said other 40 a of the firstpair of in-coupling diffractive optical elements to the first region 22a of the second out-coupling diffractive optical element 20 and fromsaid other 30 b of the second pair of in-coupling diffractive opticalelements to the second region 12 b of the first out-coupling diffractiveoptical element 10.

In box 301, the first pattern of light 5 a of the first wavelength λ₁ isemitted from the first region 12 a of the first out-coupling diffractiveoptical element 10 and the second pattern of light 5 b of the secondwavelength λ₂ is emitted from the second region 12 b of the firstout-coupling diffractive optical element 10 adjacent to the first region12 a. Meanwhile, in box 302, light of the first wavelength λ₁ in thesecond pattern 5 b is emitted from the first region 22 a of the secondout-coupling diffractive optical element 20 and light of the secondwavelength λ₂ in the first pattern is emitted from a second region 22 bof the second out-coupling diffractive optical element 20 adjacent tothe first region.

In box 401, the first patterns of light emitted from the first region 12a of the first out-coupling diffractive optical element 10 and from thesecond region 22 b of the second out-coupling diffractive opticalelement 20 are superposed and aligned with each other. Meanwhile, in box402, the second patterns of light emitted from the second region 12 b ofthe first out-coupling diffractive optical element 10 and from the firstregion 22 a of the second out-coupling diffractive optical element 20are also superposed and aligned with each other. If the first and secondpatterns of light are spatially continuous with each other, they cancombine to form a single pattern, such as a single still image or asingle frame of a video sequence, in a field of view which is both widerand brighter than if just one of the first and second patterns werepresent. Whereas boxes 301, 302, 401 and 402 are essential features ofthis method, boxes 101, 102, 201 and 202 are only preferred features.

The term ‘comprise’ is used in this document with an inclusive not anexclusive meaning. That is any reference to X comprising Y indicatesthat X may comprise only one Y or may comprise more than one Y. If it isintended to use ‘comprise’ with an exclusive meaning then it will bemade clear in the context by referring to ‘comprising only one’ or byusing ‘consisting’.

In this brief description, reference has been made to various examples.The description of features or functions in relation to an exampleindicates that those features or functions are present in that example.The use of the term ‘example’ or ‘for example’ or ‘may’ in the textdenotes, whether explicitly stated or not, that such features orfunctions are present in at least the described example, whetherdescribed as an example or not, and that they can be, but are notnecessarily, present in some of or all other examples. Thus ‘example’,‘for example’ or ‘may’ refers to a particular instance in a class ofexamples. A property of the instance can be a property of only thatinstance or a property of the class or a property of a sub-class of theclass that includes some but not all of the instances in the class. Itis therefore implicitly disclosed that a feature described withreference to one example but not with reference to another example, canwhere possible be used in that other example but does not necessarilyhave to be used in that other example.

Although embodiments of the present invention have been described in thepreceding paragraphs with reference to various examples, it should beappreciated that modifications to the examples given can be made withoutdeparting from the scope of the invention as claimed.

Features described in the preceding description may be used incombinations other than the combinations explicitly described.

Although functions have been described with reference to certainfeatures, those functions may be performable by other features whetherdescribed or not.

Although features have been described with reference to certainembodiments, those features may also be present in other embodimentswhether described or not.

Whilst endeavouring in the foregoing specification to draw attention tothose features of the invention believed to be of particular importanceit should be understood that the Applicant claims protection in respectof any patentable feature or combination of features hereinbeforereferred to and/or shown in the drawings whether or not particularemphasis has been placed thereon.

1. An apparatus comprising: a first out-coupling diffractive opticalelement and a second out-coupling diffractive optical element, whereineach of the first and second out-coupling diffractive optical elementscomprises: a first region having a first repeated diffraction spacing,d1, and a second region adjacent to the first region and having a secondrepeated diffraction spacing, d2, different from the first spacing, d1;wherein the first region of the first out-coupling diffractive opticalelement is superposed on and aligned with the second region of thesecond out-coupling diffractive optical element; and the second regionof the first out-coupling diffractive optical element is superposed onand aligned with the first region of the second out-coupling diffractiveoptical element.
 2. An apparatus according to claim 1, wherein the firstand second out-coupling diffractive optical elements are bothsubstantially rectangular and have a pair of long edges and a pair ofshort edges, and a division between the first region and the secondregion of the first and second out-coupling diffractive optical elementsis located substantially equidistant between the pair of short edges. 3.An apparatus according to claim 1, wherein the first and secondout-coupling diffractive optical elements are both diffraction gratings,wherein the first region of each grating comprises rulings of the firstspacing, d1, the second region of each grating comprises rulings of thesecond spacing, d2, and the rulings of the first region of each gratingare substantially parallel to the rulings of the second region of thesame grating.
 4. An apparatus according to claim 1, wherein the firstand second out-coupling diffractive optical elements are bothdiffraction gratings, wherein the first region of each grating comprisesrulings of the first spacing, d1, the second region of each gratingcomprises rulings of the second spacing, d2, and the rulings of thefirst region of each grating are substantially perpendicular to therulings of the second region of the same grating.
 5. An apparatusaccording to claim 1, further comprising: a first pair of in-couplingdiffractive optical element having the first repeated diffractionspacing, d1, and configured to direct light to the first region ofrespective ones of the first and second out-coupling diffractive opticalelements; and a second pair of in-coupling diffractive optical elementhaving the second repeated diffraction spacing, d2, and configured todirect light to the second region of respective ones of the first andsecond out-coupling diffractive optical elements.
 6. An apparatusaccording to claim 5, further comprising at least one intermediateoptical element configured to transmit light from a respective one ofthe in-coupling diffractive optical elements to a region of a respectiveone of the out-coupling diffractive optical elements having the samespacing as the respective one of the in-coupling diffractive opticalelements.
 7. An apparatus according to claim 6, further comprising: atleast one intermediate optical element configured to transmit light froma respective one of the in-coupling diffractive optical elements to aregion of a respective one of the out-coupling diffractive opticalelements having the same spacing as the respective one of thein-coupling diffractive optical elements, wherein the first and secondout-coupling diffractive optical elements are both substantiallyrectangular and have a pair of long edges and a pair of short edges, anda division between the first region and the second region of the firstand second out-coupling diffractive optical elements is locatedsubstantially equidistant between the pair of short edges, wherein thefirst and second out-coupling diffractive optical elements are bothdiffraction gratings, wherein the first region of each grating comprisesrulings of the first spacing, d1, the second region of each gratingcomprises rulings of the second spacing, d2, and the rulings of thefirst region of each grating are substantially parallel to the rulingsof the second region of the same grating, wherein the intermediateoptical element is positioned along one of the short edges of therespective one of the out-coupling diffractive optical elements.
 8. Anapparatus according to claim 6, further comprising: at least oneintermediate optical element configured to transmit light from arespective one of the in-coupling diffractive optical elements to aregion of a respective one of the out-coupling diffractive opticalelements having the same spacing as the respective one of thein-coupling diffractive optical elements, wherein the first and secondout-coupling diffractive optical elements are both substantiallyrectangular and have a pair of long edges and a pair of short edges, anda division between the first region and the second region of the firstand second out-coupling diffractive optical elements is locatedsubstantially equidistant between the pair of short edges, wherein thefirst and second out-coupling diffractive optical elements are bothdiffraction gratings, wherein the first region of each grating comprisesrulings of the first spacing, d1, the second region of each gratingcomprises rulings of the second spacing, d2, and the rulings of thefirst region of each grating are substantially perpendicular to therulings of the second region of the same grating, wherein theintermediate optical element is positioned along one of the long edgesof the respective one of the out-coupling diffractive optical elements.9. A monocular near-eye display comprising: an apparatus according toclaim 5; a first optical projection engine configured to projectpolychromatic light into the first and second in-coupling diffractiveoptical elements which are respectively configured to direct light tothe first region of the first out-coupling diffractive optical elementand to the second region of the second out-coupling diffractive opticalelement; and a second optical projection engine configured to projectpolychromatic light into the first and second in-coupling diffractiveoptical elements which are respectively configured to direct light tothe first region of the second out-coupling diffractive optical elementand to the second region of the first out-coupling diffractive opticalelement.
 10. A binocular near-eye display comprising: two apparatusesaccording to claim 5; a first optical projection engine configured toproject polychromatic light into the first and second in-couplingdiffractive optical elements which are respectively configured to directlight to the first region of the first out-coupling diffractive opticalelement and to the second region of the second out-coupling diffractiveoptical element of a first one of the two apparatuses; a second opticalprojection engine configured to project polychromatic light into thefirst and second in-coupling diffractive optical elements which arerespectively configured to direct light to the first region of the firstout-coupling diffractive optical element and to the second region of thesecond out-coupling diffractive optical element of a second one of thetwo apparatuses; and at least one additional optical projection engineconfigured to project polychromatic light into the first and secondin-coupling diffractive optical elements which are respectivelyconfigured to direct light to the first region of the secondout-coupling diffractive optical element and to the second region of thefirst out-coupling diffractive optical element of at least one of thetwo apparatuses.
 11. A binocular near-eye display according to claim 10,wherein each of the two apparatuses has a respective midpoint, and aseparation between the midpoints of the two apparatuses is adjustable,to accommodate different interpupillary distances of different users.12. A binocular near-eye display according to claim 10, wherein the atleast one additional optical projection engine comprises: a thirdoptical projection engine configured to project polychromatic light intothe first and second in-coupling diffractive optical elements which arerespectively configured to direct light to the first region of thesecond out-coupling diffractive optical element and to the second regionof the first out-coupling diffractive optical element of the first oneof the two apparatuses; and a fourth optical projection engineconfigured to project polychromatic light into the first and secondin-coupling diffractive optical elements which are respectivelyconfigured to direct light to the first region of the secondout-coupling diffractive optical element and to the second region of thefirst out-coupling diffractive optical element of the second one of thetwo apparatuses.
 13. A binocular near-eye display according to claim 11,wherein the at least one additional optical projection engine isconfigured to project polychromatic light by temporal or spatialinterlacing into the first and second in-coupling diffractive opticalelements which are respectively configured to direct light to the firstregion of the second out-coupling diffractive optical element and to thesecond region of the first out-coupling diffractive optical element ofboth of the two apparatuses.
 14. A method comprising: emitting a firstpattern of light of a first wavelength from a first region of a firstout-coupling diffractive optical element and a second pattern of lightof a second wavelength from a second region of the first out-couplingdiffractive optical element adjacent to the first region; emitting lightof the first wavelength in the second pattern from a first region of asecond out-coupling diffractive optical element and light of the secondwavelength in the first pattern from a second region of the secondout-coupling diffractive optical element adjacent to the first region;superposing and aligning the first patterns of light emitted from thefirst region of the first out-coupling diffractive optical element andfrom the second region of the second out-coupling diffractive opticalelement; and superposing and aligning the second patterns of lightemitted from the second region of the first out-coupling diffractiveoptical element and from the first region of the second out-couplingdiffractive optical element.
 15. A method according to claim 14, furthercomprising: projecting polychromatic light with the first pattern intoone of a first pair of in-coupling diffractive optical elements with afirst repeated diffraction spacing corresponding to the first wavelengthand into one of a second pair of in-coupling diffractive opticalelements with a second repeated diffraction spacing corresponding to thesecond wavelength; projecting polychromatic light with the secondpattern into the other of the first pair of in-coupling diffractiveoptical elements with the first repeated diffraction spacing and intothe other of the second pair of in-coupling diffractive optical elementswith the second repeated diffraction spacing; transmitting the firstpattern of light from said one of the first pair of in-couplingdiffractive optical elements to the first region of the firstout-coupling diffractive optical element and from said one of the secondpair of in-coupling diffractive optical elements to the second region ofthe second out-coupling diffractive optical element; and transmittingthe second pattern of light from said other of the first pair ofin-coupling diffractive optical elements to the first region of thesecond out-coupling diffractive optical element and from said other ofthe second pair of in-coupling diffractive optical elements to thesecond region of the first out-coupling diffractive optical element.